Question 423703
I believe your question is

(r^2-5r+6)/(r^2-4)
r^2-3r-2r+6=r(r-3)-2(r-3)=(r-2)(r-3)  you have negative in the center and positive number so both have to be negative
r^2-4=(r+2)(r-2)

so we have {(r-2)(r-3)}/(r-2)(r+2)

r-2 at bottom and top cancels
we have (r-3)/(r+2)

I believe for all r +-2  
if r=-2 we have -2-3 divided by 0=0
if r=2  we have 2-3  divided by 2+2=  -1/4
hope this makes sense